Monthly Archives: August 2011

So another ten days have gone by, with me turning the router on and off to reset it when its NAT table fills up, which causes slow connections and site dropouts – despite some connections continuing to work.

After doing more reading and testing, I was thoroughly convinced that this is a problem with the router. Whether its a limitation of firmware design, memory, whatever, I don’t know. It’s a limitation, and it makes our internet connection painful to use.

So I gathered a bunch of data, video recording of the lights on the modem, printout of modem’s signal status page, dumps of the `netstat` command in various states of working, slow and ridiculously slow, and sent them all in to big pond for a technical support request. The main part of the request is this:

If I bought a device as crappy as this from a retail shop, like Harvey Normal or Office Works, I’d be well within my rights to return it as faulty, get a refund and buy a different model. However, since Telstra Bigpond provide the equipment, this process is *far* more difficult.

It appears that there are two solutions:

Disable NAT in the CGD24N, effectively using it only as a modem, and buy my own wireless router; or

Exchange the CGD24N for a Motorola single port modem, and buy my own wireless router.

They both suck, because of the obvious step of “buy my own wireless router” which is at my cost.

With that being the punch line, I sent all of that into to BigPond support. They asked me to do some line checks, which all passed, of course, because the problem is in the router, not the modem or the line. But to eliminate the possibility of a faulty unit, or faulty line, I had to get a technician out to check the line. Which happens during business hours, costing my time and more money!

Here comes the Technician

So, along comes the technician. A friendly fellow. Checks the line status. All good, no surprises. He marks it as a faulty router and replaces it. Let’s see how it goes.

This Netgear CGD24N router has really been giving me a headache. We have several network devices, more than some, but not what I call extreme. There are three people living in our house, and we have:

2 x laptop computers

2 x desktop computers

2 x iPhones

1 x iPad

1 x AppleTV

There’s a few other devices, like a network printer, but they aren’t heavy on internet traffic.

After doing quite a bit of reading on the Whirlpool forum, it’s clear that there is a known problem with the Netgear CGD24N router with its Network Address Translation (NAT), which is a really important function of a router to share an internet connection with multiple devices (in layman’s terms).

Another guy “Extreame” has started his own forum in competition to Whirlpool (it seems, not as good though… too much flashy useless stuff) and has some good information too. He seems to be quite the expert on cable modems and recommends turning NAT off and buying your own wireless router.

The Symptoms

After using the router for a while, certain web pages will completely time out. It looks like a line drop out at first, but then you discover that some pages continue to work while others don’t. When accessing a web site, the browser tends to keep a connection to the server open for a subsequent request (perhaps some javascript, images, etc). These pages continue to work. Other pages don’t.

Logging in to the router, I can see that the connection is still good. (Also proven by the web pages that do work) and that you can ping the outside world from the router. Frustrating.

Further Testing

The `netstat` command on Mac (and similar on Linux / Windows) show the status of your network connections. Typically, when everything really starts to slow right down, I see a lot of this in my netstat output:

What’s all this SYN_SENT business? I haven’t seen that before. After looking into it, this is what happens when your computer is trying to make a connection to a remote server but no response has been received from the server. This is consistent with the NAT table being full, such that the router cannot return the packets from the server back to the computer. This is also consistent with why some sites continue to work while others time out.

According to the Whirlpool status page, the CGD24N has a NAT routing table size of 1024. So that’s 1024 connections, should be enough for about 8 devices right? Let’s think about it. Each mail account has probably 2 connections (send via smtp and receive via imap/pop). Each web site you go to typically has about 5 connections from modern browsers like Firefox and Safari. Other applications, such as iTunes, that access the internet all make their own connections too.

The result is, that you don’t need to have too many windows or tabs open at once to run into this limit. So is 1024 normal? small?

Proving the point

I managed to get an ssh connection to a computer at my work, and ran a SOCKS proxy over the connection. After adding the SOCKS proxy to my network configuration, all of a sudden, my connections were all working. A few more hops to the internet, and doubly using my work’s internet connection, which isn’t an acceptable solution, but it proves that bypassing the NAT in the router and making all requests through a proxy (which are sharing one established connection) gives no network problems at all.

We just signed up for a Telstra Bigpond cable connection. I was previously with Internode, who I was very happy with, for many years, and it was a big decision to leave. Basically, we changed because of more data, less price, and most importantly faster downloads. Previously, I’d had good experience with ADSL2, but our house we moved into a year and a half ago has a crappy phone line where we could only get around 4 Mb/s, which didn’t cut it for our increasing internet video usage. (Apple TV and Youtube more and more these days).

So, along comes with installer with a Netgear CGD24N cable modem and router. It’s got a two nice features, our old modem didn’t have:

Wireless N

Guest network

Great. BUT, there’s always a BUT. These are the issues I discovered straight off:

I spent time on the phone to Netgear chasing the manual. They were very unhelpful, claiming it was a model specific to Telstra (despite being on their website with technical specifications). So my first support call to Bigpond was to get the manual. At least they provided it to me. Thanks.

So far, the internet connection is largely very good. Downloads are smashing fast. Speedtest tops about 28Mb/sec from a wired connection to the router. And HD videos on the Apple TV stream nearly instantly.

In the main, I’m happy with the connection, but I have a feeling this little router is going to annoy the crap out of me.